Are you confined to researching this on the internet? Cant you just measure them? Are you running out of time on an eBay auction?
With a little research, I found
THIS bike with a stock stem and IRO bars. Then I went to the IRO website and found the only set of dropbars they offer is 26mm. I would go as far as to assume the stock bars are 26mm... but I would still measure them LOL. Even if the stem is a 25.4mm, 26mm bars still fit in a 2-pc stem.